Retrofitted hybrid drive systems are known in the art. A motor-generator device that can retro-fitted and installed on an internal combustion powered vehicle to add electric motive force and power to the vehicle, and thereby convert the vehicle to a hybrid, is disclosed in Perry, et al., “Machine for Augmentation, Storage, and Conservation of Vehicle Motive Energy,” U.S. Pub. No. 2012/0215389, which is incorporated herein by specific reference for all purposes. Earlier hybrid drive systems also are disclosed in Lynch, et al, U.S. Pat. No. 4,165,795 and Kawakatsu, U.S. Pat. No. 4,335,429, which are incorporated herein by specific reference for all purposes as well.
However, prior art systems still can be difficult to install, and cause drag due to the presence of magnetic fields. The magnets also attract and collect road dust and debris, causing the motor to become dirty and inefficient.